1. Field of Invention
The present invention relates generally to disease prevention in livestock, and, more specifically, to the prevention of sudden death syndrome in broiler breeder strain poultry.
2. Background
Sudden death syndrome (SDS), also known as Acute Death Syndrome or "Flip-Over," is characterized by high mortality (12-18%) in breeder hens during a period of high metabolic stress between the onset of lay and peak egg production without any premonitory signs. Chickens and turkeys that die of SDS are most often found lying on their backs. First recognized in Australia in the late 1970's and in Europe and U.S. flocks in the 1980's, a specific etiology for the syndrome has not been identified. The disease is known, however, to be a cardiovascular disorder and is evidenced by abnormal cardiac traits and lesions. Though mortality has been associated with the effects of an imbalance or deficit of potassium, calcium or phosphorus on metabolism during egg production, therapies directed to these areas have not proved successful.
Changing epizootiology suggests that SDS is developing into a major worldwide enzootic threat to the poultry industry. Exacerbating the stress associated with the onset of lay is the high growth rate and high metabolic demands of today's genetically engineered birds. The desire to achieve rapidly growing lean strains of meat poultry and the demands from processors to increase yields by reducing the overall size of visceral organs has meant a selection of strains susceptible to sudden death syndrome. To put it in perspective, the age to slaughter and the amount of feed required to produce a given quantity of chicken meat has been more than halved since the early 1950's. See Havenstein, G. B., P. R. Ferket, S. E. Scheldeler and B. T. Larson, Growth, Livability and Feed Conversion of 1957 vs. 1991 Broilers When Fed "Typical" 1957 and 1991 Broiler Diets, Poultry Science, Vol. 73, pp. 1785-1794 (1994). In the early 1950's the average length of time required to grow a broiler chicken to a 4 pound harvest weight exceeded 15 weeks. Through genetic selection, this time period has been reduced to a current average of about 6 weeks. Consequently, bird metabolic events that are needed to produce a unit of poultry meat have been squeezed into a shorter time period, creating a high metabolic demand in today's bird. Such metabolic demand is further elevated by environmental factors, such as low and high ambient temperature, and disease. As a bird having a high metabolic demand possesses a higher oxygen requirement, severe stress is placed on the bird's cardiovascular support system.
The broiler breeder experiences a demanding combination of the aforementioned stresses. While it is genetically engineered to possess a high growth rate, it must also undergo the stress of egg production.
In low total mortality flocks, a 1 to 2% incidence of SDS has a major economic impact. Thus, there exists a need to lower the incidence of sudden death syndrome among the broiler breeder subset of the poultry populace. The present inventors have surprisingly discovered that a carnitine supplemented diet for broiler breeder strain poultry fed early in the egg production cycle, such as during the stressful period just preceding the onset of lay and continuing to peak egg production, prevents the cardiac malformations associated with SDS in the targeted poultry demographic.
Heretofore, carnitine in poultry diet has been reported to have no beneficial effect on feed intake, body and abdominal fat weight or on carcass or liver lipid levels in growing broilers (Cartwright, Poultry Science, Vol. 65, Suppl. 1, p. 21, 1986). Dietary carnitine has been shown to retard ethanol metabolism in broilers (Smith et al., Poultry Science, Vol. 71, Suppl. 1, p. 64, 1992). Carnitine in poultry diet has also been shown, in U.S. Pat. No. 5,362,753, to increase the hatchability of eggs laid by breeder hens. It should be noted, however, with respect to the latter reference, that the primary efficacy of that invention relates, as shown in Table 1 of the '753 patent, to hatchability at the time of efficient egg production, i.e., at peak egg production and beyond. The '753 reference must further be noted to concern increasing the carnitine concentration in the egg such as to allow the embryo to more easily employ the stored fat of the egg. Nothing within the four corners of the '753 reference teaches or suggests any benefit to the breeder hen who has consumed the carnitine supplemented ration.
Unrelated to poultry, carnitine has been used as a supplement in pig diets (U.S. Pat. Nos. 5,124,357 and 5,192,804 and PCT Publication WO 98/24328), a smolting feed for salmon (U.S. Pat. No. 5,722,346) and in a catfish diet (U.S. Pat. No. 5,030,657). The use of carnitine in the treatment of heart failure or myocardial ischemia is discussed in U.S. Pat. No. 4,075,352 and PCT Publication WO 98/43617.
Notwithstanding the known uses of carnitine, the prior art wholly fails to teach or suggest as disclosed and claimed herein a carnitine supplemented diet fed to broiler breeder strain poultry early in the egg production cycle to prevent sudden death syndrome.